1. Field of the Invention
The present invention relates to a hollow golf club head that is capable of increasing the launch angle of a hit ball and increasing the distance of the hit ball.
2. Description of the Related Art
Recently, there have been proposed hollow golf club heads constructed such that elastic deformation is generated at a crown part as well as a face part when hitting a ball, whereby the launch angle and distance of the hit ball are increased. Examples of such hollow golf club heads are disclosed in JP-A-2003-52866, JP-A-2003-79768, JP-A-2003-88601, and JP-A-2005-137788.
The golf club head disclosed in JP-A-2003-52866 is a metal hollow golf club head including a face part, a sole part, a side part, a crown part, and a hosel part, wherein at least the main portions of the crown part and the face part are integrally formed with each other, by casting, to constitute a front part, the other parts of the golf club head excluding the front part are also integrally formed with each other to constitute a back part, and the front part and the back part are joined to each other.
The golf club head disclosed in JP-A-2003-79768 is a metal hollow golf club head including at least a face part, a sole part, a side part, and a crown part, wherein the metal material forming the crown part has the lowest modulus of longitudinal elasticity.
The golf club head disclosed in JP-A-2003-88601 is a metal hollow golf club head including a face part, a sole part, a toe-side side part, a heel-side side part, back-side side part, a crown part, and a hosel part, wherein the crown part is provided with a plurality of grooves, which extend from the toe-side side part toward the heel-side side part.
The golf club head disclosed in JP-A-2005-137788 is a hollow golf club head including a face part having a face surface, by which a ball is hit, and a head body part extending to the rear of the head along the rear surface of the face part, wherein the head body part includes a crown part, a sole part, and a side part, which form an upper head part, a lower head part, and a side head part, respectively, and the crown part includes a front crown part forming a front section extending a distance corresponding to 0.15 of the crown depth-wise length Lc from the rear surface of the face part and a rear crown part forming a rear section extending 0.30 or more, moreover, 1.0 of the crown depth-wise length Lc from the rear surface of the face part, the front crown part having a rigidity smaller than that of the rear crown part.
However, it is required that the golf club heads according to JP-A-2003-52866, JP-A-2003-79768, JP-A-2003-88601, and JP-A-2005-137788 be improved to increase launch angle.